Arsenate of lime product and process of making same



Patented Nov. 27, 1923.

UMTED stares aste PATENT OFFICE.-

LOUIS CHARLES DREFAHL, OF LAKEWOOD, AND CHARLES H. SAKRYD, CLEVELAND,

OHIO, ASSIGNORS TO THE A CORPORATION OF OHIO.

GRASSELLI CHEMICAL COMPANY, OF CLEVELAND, OHIO,

AESENATE OF LIME PRODUCT AND PROCESS OF MAKING SAME.

Io Drawing.

' To allwhbmz't may concern:

Be it known that we, (1) LoUIs C. DREFAHL and (2) CHARLES H. SAKRYD, citizens of the United States, residing at (1) Lakewood,

'6 (2) Cleveland, in the county of Cuyahoga and State of Ohio, have invented certain slurry of suitable strength, the reaction be-,

ing carried out at the ordinary prevailing room'temperature. The resulting precip1- tate is separated from the vehicle in which it has been precipitated in any suitable manner, such as, by vfilter ressing, whereby arsenate of lime paste is ormed which may be sold as such, but more commonly the paste is further dried and pulverized to produce a dry powdered arsenate of lime product.

It has been found that the presence of free lime in the product reduces its water soluble arsenic acid content and improves-its stability and it has therefore become customary in the manufacture of arsenate of lime for 85 insecticidal use to employ a considerable ex cess of lime slurry in the reaction so that the product will contain. free lime. The free lime soprovided in theproduct varies in' amount up to as hi h as '5 per cent or more.

' 40 By operating in t is manner it has been possible to produce products meeting in general the. requirements of the national and- State insecticide and fungicide boards with regard to physical properties, total arsenic 4!! acid content and water soluble arsenic acid content. I

- In the preparation of arsenate of lime as described above the watersoluble arsenicw acid contentof the product may be decreased and the stability of the product improved by increasing-the amount of excess of lime Applicationfiled January 30, 1922. Serial No. 532,833.

employed but this in turn results in a decrease in the total arsenic acid content of the product which normally is only slightly above the minimum limit. On the other hand if it-is attempted to increase the total arsenic acid content of the product by decreasing the amount of-excess of lime employed then the stability of the product is lessened and the water soluble arsenic acid content is increased. The process has been found to be rather diflicult to control so as to give a uniform product and frequently results in a product which exceeds the permissible limits with regard to total arsenic acid content and water soluble arsenic acid content.

Our experience with the foregoing process and product has led us to believe that the calcium arsenate in the product is very loosely bound, (probably consistin of a mixture of mono, i, tri, and even ca cium tetra arsenate.

In studying the process with a view to the production of a more stable commercial arsenate of lime, a large amount of research has been directed to a determination of the eflect of the temperature employed during precipitation or neutralization.

We have found that at an elevated temperature (120 F. or higher) it ispossible to make a product which is very much more stable than 'the commercial product heretofore produced and which also has a larger total arsenic acid content. Upon'th'e' basis of this discovery we have devised-a process for the manufacture of commercial arsenate of lime having improved propertieapith' respect to total arsenic acid content, water soluble arsenic acid content, and stability, the physical properties of which are as satisfactory as thecorrespondi'ng physical properties of commercial calcium arsenate produced by cold precipitatiori. I An example of our process is as follows:

A solutionof arsenic acid testing about'20 per cent As,0, isslowly addedwith stirring to a lime slurry testing about. 10 per cent CaO while maintaining the reaction mixture at a temperature of from 140 F. to 160 F.

The ratio of solids to liquids in the complete'd batch is about one to twelve. The

rated, dried and powdered in the usual man- I This process .is capable of considerable variation and it is to be understood that the invention is not limited tothe details set forth in the example given above. The arsenic acid solution and the lime slurry employed may vary in concentration but a concentrated solution and slurry are of course preferred since they reduce the bulk of liquid to be handled. On the other hand the reagents must not be so concentrated as to prevent complete reaction or detrimentally affect the physical properties of the product.

It has been stated that a slight excess of lime is employed since it is thought that the stability of the product under storage is thus improved. The excess of lime however is not essential since the product is quite stable without it.

The temperature at which the reaction is carried out mayvary from 120 F. to 200 F. or even 212 F. Satisfactory results have been obtained at temperatures as low as 120 F. and as high as 212 F. At temperatures outside of the range from 140 F. to 160 F. there is a tendency for the physical properties of the product to be" less satisfactory than when precipitation is carried out at from 140 F. to 160 F.

use

Has

The product as prepared by ,our process, when reasonably pure reagents have been employed, besides meeting the Government specificationswith regard to physical properties contains considerably more than 40 per cent of arsenic acid calculated as AS205 stability "are illustrated in the following table.

Product containing about per cent total A8205.

Water soluble arwatei-r soh-lble senic acid con- Semc acld Temperature of. t M 1 u! t d tent calculated precipitation. 53 f g as AS205, after made 15 months storage.

80 F. 77 per cent. 2. 41 per cent.

90 F. .78 2:01 140 F. 24 29 180 F. .14 .34

about per cent total As O produced by hot precipitatiom as compared with'a similar product produced by cold precipitation is indicated by the following data.

Water soluble ar- Temperature of tent calculated precipitation. g sk if figg as AS205, after made 15 months storage. I

Atmospherictem- 2 to 2 per cent.

5 to 10 per cent. 92

perature 180 F.

We claim:

1. Process of making a stable, water-insoluble arsenate of lime product which comprises precipitating calcium arsenate in a medium maintained at a temperature of from 120 F. to 160 F.

2. Process of making calcium arsenate Water soluble an i i which comprises reacting upon a water soluble compoundof arsenic with a water soluble compound of calcium in a reaction mixture maintaine at a temperaure of from 120 F. to 160 F.

3. Process of making calcium arsenate which comprises reacting upon calcium hydroxid with a solution of arsenic acid in a reaction mixture maintained at a temperature of from 120 F. to 212 F.

4. Process of making calcium arsenate which comprises reacting upon .calcium hy-,

droxid with arsenic acid in a reaction mixture maintained at a temperature of from a stable arsenate of 4 which comprises'neutralizing a lime slurry 1 with a solution of arsenic acid while maintaining the reaction mixture at a temperature of from 140 to 160 F. v

8. Process of making calcium arsenate which comprises adding a solution of arsenic acid containing about 20% As O to a lime slurry containing about 10% Cat) whlle maintaining the reaction mixture at a temperature of from 120 F. to 212 F.

9. Process of making calcium arsenate which comprises adding a solution of arsenic'acid containing about 20% As O to a lime slurry containing about 10% Ca() while maintaining the reaction mixture at 4 from to F.

The stability of a product containing A stable arsenate of lime product contalnmg atleast 40 per cent bf AS205, said product being stable under storage and conice taining less soluble arsenic than a product containing the same quantity of A8 0 produced by the interaction of an arsenic acid solution and a lime slurry at a temperature less than 120 F.

11. Arsenate of lime product containing at least 40 per cent of AS205, Said productbeing more stable under storage than arsenate of lime produced by the interaction of arsenic acid solution and lime slurry at ordinary room temperatures.

12. Arsenate of lime such as may be prepared by the hereindescribed process which comprises reacting upon a lime slurry with a solution of arsenic acid while maintaining the reaction mixture at a temperature 'of from 120 F. to 212 F.

In testimony whereof, we afiix oursignatures.

LOUIS CHARLES DREFAHL. CHARLES H. SAKRYD. 

